The present invention relates to a control system of a torque distribution to left and right driving wheels of a motor vehicle, and more particularly to the control system in which an output torque of a transmission is distributed to the left and right rear driving wheels in accordance with driving conditions of the vehicle.
The motor vehicle is provided with a differential between the left and right wheels. If an input torque to the differential is large at driving on a slippery road, the wheels are liable to slip. Accordingly, there is provided a differential operation restricting device for restricting the differential operation of the differential which is operated in response to the input torque. The restricting device previously operates to restrict the differential operation, thereby preventing the wheels from slipping. In a differential operation restricting device having a mechanical engaging device, engaging force for restricting the operation steeply increases at a predetermined input torque. Consequently, when an accelerator pedal of the motor vehicle is depressed at cornering, running behavior of the vehicle may suddenly change due to a rapid change of the engaging force. In order to solve such a problem, a fluid operated multiple-disk friction clutch has been provided. The engaging force of the clutch is continuously changed in accordance with the differential input torque, thereby smoothly controlling the differential restricting clutch torque.
Japanese Patent Application Laid-Open 63-184526 discloses such a differential operation control system. The system operates to restrict the differential operation when vehicle speed is smaller than a predetermined value in accordance with vehicle driving torque which is the differential input torque.
By the conventional system, the slipping of the wheels can be prevented to ensure driveability of the vehicle. However, since the differential restricting torque is controlled only by the differential input torque, the differential operation is largely restricted when the input torque is large. Accordingly, straight-ahead running and steering characteristics are deteriorated. In particular, when the vehicle negotiates a curve of an uphill road having a high friction coefficient, the differential operation is excessively restricted.